Methods for manufacturing a display device

ABSTRACT

Methods for manufacturing a display device are provided. A representative method includes: providing a thin film transistor (TFT) substrate having a plurality of sub-pixel locations and a plurality of TFTs corresponding to the plurality of sub-pixel locations; providing a carrier substrate supporting a plurality of light emitting diodes (LEDs), wherein each of the plurality of LEDs has a first electrical contact and a second electrical contact; transferring the plurality of LEDs from the carrier substrate to the TFT substrate, with at least two of the plurality of LEDs being disposed at one of the plurality of sub-pixel locations; and fixing positions of the plurality of LEDs with respect to the TFT substrate. The method also may include: determining that a first LED of the plurality of LEDs is defective; and electrically isolating the first electrical contact of first LED from a first electrode of the display device.

CROSS-REFERENCE

This utility patent application claims the benefit of and priority toU.S. provisional application 62/350,169, filed on 14 Jun. 2016, which isincorporated by reference herein in its entirety.

BACKGROUND Technical Field

The disclosure relates to display devices and, in particular, to methodsfor manufacturing such display devices.

Description of the Related Art

In an effort to meet consumer demand for high quality display devices,industry trends have turned to light emitting diode (LED) technology.Although considered a relatively mature technology in general,advancements in LEDs, such as through the development of micro-LEDs(sometimes referred to as “mLEDs” or “μLEDs”) have drawn attention.However, numerous technical challenges exist in their implementation.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a schematic, plan view of an example embodiment of a displaydevice, showing a plurality of sub-pixels.

FIG. 2 is a schematic, cross-sectional view of an example embodiment ofa display device, showing detail of a sub-pixel, as viewed along sectionline 2-2 of FIG. 1.

FIGS. 3-5 are flowcharts depicting example embodiments of a method formanufacturing a display device.

FIGS. 6A and 6B are schematic, cross-sectional views of exampleembodiments of thin film transistor (TFT) substrates.

FIG. 7 is a schematic, cross-sectional view of an example embodiment ofa carrier substrate.

FIG. 8 is a schematic, cross-sectional view of an example embodiment ofa TFT substrate showing detail of the insulating layer in providingmechanical clearance with a transfer head.

FIGS. 9 and 10 are schematic diagrams depicting example embodiments oftesting of LEDs disposed on a carrier substrate.

FIGS. 11A and 11B are schematic, cross-sectional views of an exampleembodiment of a carrier substrate showing removal of LEDs.

FIGS. 12A and 12B are schematic, cross-sectional views of exampleembodiments of TFT substrates showing placement of LEDs.

FIGS. 13A and 13B are schematic diagrams depicting example embodimentsof testing of LEDs disposed on TFT substrates.

FIG. 14 is a schematic, cross-sectional view of an example embodiment ofa TFT substrate with a deposited filling insulator.

FIG. 15 is a schematic diagram showing an example embodiment of arepair.

FIG. 16 is a schematic, cross-sectional view of an example embodiment ofa TFT substrate with a deposited first electrode.

FIG. 17A is a schematic, plan view of an example embodiment showing afirst electrode.

FIG. 17B is a schematic, plan view of another example embodiment showinga first electrode.

FIG. 18 is a schematic, cross-sectional view of an example embodiment ofa TFT substrate with a light guide layer.

FIG. 19 is a schematic, cross-sectional view of an example embodiment ofa TFT substrate with a wavelength conversion layer.

FIG. 20 is a schematic, cross-sectional view of an example embodiment ofa TFT substrate with a color filter.

FIG. 21 is a schematic, cross-sectional view of another exampleembodiment.

FIG. 22 is a schematic view of another example embodiment showingremoval of a flip-chip type LED.

FIG. 23 is a schematic, plan view of another example embodiment.

FIG. 24 is a schematic, cross-sectional view of another exampleembodiment of a portion of a display device.

FIG. 25 is a schematic view of another example embodiment of an LED.

DETAILED DESCRIPTION

Reference will now be made in detail to that which is illustrated in thedrawings. While the disclosure will be described in connection withthese drawings, there is no intent to limit the scope of legalprotection to the embodiment or embodiments disclosed herein. Rather,the intent is to cover all alternatives, modifications and equivalentsincluded within the spirit and scope of the disclosure.

In this regard, embodiments of a method for manufacturing a displaydevice are provided. In some embodiments, the method involves anintegrated process in which light emitting diode (LED) placement isperformed in combination with one or more of various other proceduressuch as testing, defect repair, and layer (e.g., light guide layer)formation, for example. In some embodiments, an LED is provided at asub-pixel location. In some embodiments, at least two LEDs are providedat a sub-pixel location, thereby providing component redundancy for eachsub-pixel. In the event that an LED at a sub-pixel location isidentified as being defective, the defective LED may be electricallyisolated from a first electrode of the display device, thus potentiallymitigating unwanted impacts of the defective LED while permitting theother of the LEDs to emit light. In some embodiments, a passivationlayer is formed over a defective LED to electrically isolate that LEDfrom the first electrode. In other embodiments, a laser cutting isprovided to cut off the first electrode and electrically isolate thefirst electrical contact of the LED.

FIG. 1 is a schematic, plan view of an example embodiment of a displaydevice 100, which may be used in a variety of devices, such as mobiledevices. Display device 100, only a portion of which is depicted,incorporates a plurality of sub-pixels (e.g., sub-pixels 102, 104 and106), with each of the sub-pixels including at least one LED (e.g., amicro-LED). For instance, sub-pixels 102, 104 and 106 include LEDs 112,114 and 116, respectively.

Additional detail of sub-pixel 104 is depicted in FIG. 2. Specifically,sub-pixel 104 incorporates a thin film transistor (TFT) 120, whichcontrols LED 114 in response to control signals provided by sourceelectrode and gate lines (not shown) as is known. Each of the sub-pixelsof display device 100 incorporates a TFT for controlling operation ofthe corresponding LED to produce light (e.g., light produced by LED 114is depicted by arrow 122). In this embodiment, electrical contacts (124,126) of LED 114 are provided on a bottom 128 of the LED opposite alight-emitting top 130 of the LED.

The LEDs and TFTs of display device 100 are supported by a TFT substrate138 upon which the TFTs are formed. The TFT substrate could be rigid orflexible. The material of the TFT substrate could be glass, plastic(Polyimide (PI) or PET), for example. A cover (e.g., a glass cover, apolarizer, a barrier film or capping layer (inorganic-organic-inorganiclayers)) 140 also is provided as an outer protective covering of thedisplay device 100.

FIG. 3 is a flowchart depicting an example embodiment of a method 150for manufacturing a display device, such as display device 100 of FIG.1, for example. As shown in FIG. 3, method 150 may be construed asbeginning at block 152, in which a TFT substrate is provided thatincorporates a plurality of sub-pixel locations (i.e., locations atwhich sub-pixels are to be formed) and a plurality of TFTs correspondingto the sub-pixel locations. In block 154, a carrier substrate supportinga plurality of LEDs is provided. Specifically, each of the LEDs includesa first electrical contact and a second electrical contact. In block156, the plurality of LEDs is transferred from the carrier substrate tothe TFT substrate, with at least two of the plurality of LEDs beingdisposed at each of the plurality of sub-pixel locations. It should benoted that transferring of the LEDs may be performed in multipletransfer steps involving a subset of the LEDs at each step as the totalamount of the LEDs may be too large to be transferred at one time. Insome embodiments, a transfer head of pick-and-place equipment is used totransfer the LEDs from the carrier substrate to the TFT substrate. Then,as depicted in block 158, positions of the plurality of LEDs are fixedwith respect to the TFT substrate. As a result, at least two LEDs arefixed at each of the sub-pixel locations of the TFT substrate to form acorresponding sub-pixel.

Another example embodiment of a method for manufacturing a displaydevice is depicted in the flowchart of FIG. 4. As shown in FIG. 4,method 200 may be construed as beginning at block 202, in which a TFTsubstrate with a plurality of sub-pixel locations and a plurality ofTFTs is provided. In block 204, a carrier substrate supporting aplurality of LEDs is provided. Specifically, each of the plurality ofLEDs supported by the carrier substrate includes a first electricalcontact and a second electrical contact. In block 206, the plurality ofLEDs is transferred from the carrier substrate to the TFT substrate,with a corresponding one of the plurality of LEDs being disposed at eachof the plurality of sub-pixel locations. It should be noted thattransferring of the LEDs may be performed in multiple transfer stepsinvolving a subset of the LEDs at each step as the total amount of theLEDs may be too large to be transferred at one time. Thereafter, such asdepicted in block 208, positions of the plurality of LEDs are fixed withrespect to the TFT substrate. By way of example, the LEDs may be bondedto the TFT substrate with bonding material.

In block 210, a filling insulator is provided. In particular, thefilling insulator contacts sidewalls of the plurality of LEDs.

It should also be noted that, in some embodiments, prior to providingthe filling insulator, a determination may be made regarding whether afirst LED of the plurality of LEDs is defective. Responsive toidentifying that the first LED is defective, a first electrical contactof the first LED may be electrically isolated from a first electrode ofthe display device. In some embodiments, electrically isolating an LEDmay involve providing a passivation layer over and/or laser cutting anelectrical contact of the defective LED. As mentioned previously,electrical isolation of the LED in this manner may potentially mitigateunwanted impacts of the defective LED.

The process of defect detection may be performed as desired among theplurality of LEDs, and defect repair may be provided in a single processto electrically isolate multiple LEDs identified as being defective. If,however, it is determined that no LEDs are defective, the defect repairstep may be omitted.

Still another example embodiment of a method for manufacturing a displaydevice is depicted in the flowchart of FIG. 5. It should be noted thatthe flowchart of FIG. 5 includes numerous steps/processes that may beconsidered optional in some embodiments. Additionally, although shown ina particular sequence of steps/processes for purposes of expediency,various other orderings of the steps/processes may be used in otherembodiments. Further, the steps/processes described in relation to FIG.5 are described in greater detail with reference to subsequent figures.

As shown in FIG. 5, method 300 may be construed as beginning at block302, in which a TFT substrate is provided. As will be described ingreater detail with respect to FIGS. 6A and 6B, a TFT substrate may beprovided in various configurations, such as top gate TFT or bottom gateTFT. The material of active layer (channel) of a TFT may be amorphoussilicon (a-Si), metal oxide or low temperature polysilicon (LTPS), amongothers. In block 304, an insulating layer is deposited on the TFTsubstrate. Specifically, the insulating layer is provided to establishadequate clearance between the operational surfaces of transfercomponents used in transferring LEDs to the TFT substrate as will bedescribed in greater detail with respect to FIG. 8. In block 306, acarrier substrate is provided, which includes LEDs to be transferred tothe TFT substrate. An example embodiment of a carrier substrate andassociated TFTs is described later with respect to FIG. 7. Notably, oneor more of various tests may be performed on the TFT substrate and/orcarrier substrate (such as described with respect to FIGS. 9 and 10).Thereafter, such as presented in block 308, the TFT substrate andcarrier substrate are loaded onto a platform to facilitate LED transferand placement.

As shown in block 310, an array of transfer heads is positioned over theLEDs of the carrier substrate, and in block 312 the transfer heads areplaced in contact with the LEDs. Then, as presented in blocks 314 and316, the transfer heads pick up the LEDs and place the LEDs on the TFTsubstrate. The process of transferring and placing the LEDs will bedescribed in greater detail with reference to FIGS. 11A, 11B, 12A and12B.

Proceeding to block 318, the TFT substrate with the placed LEDs istransferred to a test platform to facilitate one or more of varioustests, such as photoluminescence and electroluminescence testing(described later with respect to FIGS. 13A and 13B). After determiningthat an LED is defective, the process may proceed to block 322, at whichrepair of the defective LED may be conducted (see, FIGS. 15, 23 and 24for more detail). Subsequently, the TFT substrate may be transferred toa deposition chamber such as depicted in block 324.

Beginning in block 326, positioning within the deposition chamber mayfacilitate further fabrication. Specifically, as presented in block 326(and with further description to follow in relation to FIG. 14), afilling insulator may be provided. In block 328, a first electrode ofthe display device is deposited (see, FIGS. 16, 17A and 17B). Then, suchas depicted in blocks 330 and 332, a light guide layer (FIG. 18) and awavelength conversion layer (FIG. 19) may be provided. The oppositesubstrate is then covered (with or without the incorporation of a colorfilter) as shown in block 334 (see, FIG. 20).

In FIG. 6A, an example embodiment of a TFT substrate 350 configured witha bottom gate TFT 352 is depicted. In preparing TFT substrate 350,various processes may be used. Specifically, a substrate 354 (e.g., arigid or flexible substrate) is provided upon which a metal layer (M1)layer 356 is patterned to form gate electrode and gate/scan line. A gateinsulation layer 358 is deposited, and then subsequently metal (M2)layer 362 is patterned to form source electrode, drain electrode anddata lines, following deposition of first and second passivation layers364 and 366, respectively. A channel 360 is formed in the active layerand between the source and drain electrodes. The first and secondpassivation layers 364 and 366 have a contact via 372, which is passingthrough the first passivation layer 364 and second passivation layer 366to expose at least a portion of the metal layer (M2) 362. In thisembodiment, the metal layer (M1) 356 and the metal layer (M2) 362 aremulti conductive layers. In other embodiments, the metal layer (M1) 356and the metal layer (M2) 362 could be a single conductive layer.

Also shown in FIG. 6A is reflective structure 370, which defines asub-pixel location for the placement of one or more LEDs. In thisembodiment, formation of reflective structure 370, deposition insulatinglayer 374, and then etching an opening 376 in the insulating layer toexpose the contact via 372. A metal (M3) layer 378 is then depositedwithin opening 376 to form the reflective structure and deposited withinthe contact via 372 to electrically connect to the metal layer (M2) 362.Additionally, metal layer 378 may be used to form common lines (e.g.,common line 380) for electrically connecting to a first electrode of theassociated display device. The common line 380 may provide a commonvoltage to the first electrode. An optional bonding (M4) layer 382formed of bonding material may also be provided at the sub-pixellocation over reflective structure 370 to facilitate bonding of one ormore LEDs.

Another example embodiment, in which a TFT substrate 400 configured witha top gate TFT 402, is depicted in FIG. 6B. TFT substrate 400 includes asubstrate 404 upon which a buffer layer 406 and an active layer 408 areformed. Re-crystallization (e.g., by excimer laser annealing),patterning to form the channel 410, and channel/N+ doping are performed.Gate insulation layer 412 and metal (M1) layer 414 are subsequentlydeposited and patterned to form gate electrode and gate lines.Thereafter, first and second passivation layers (420, 422) aredeposited. Depositing and patterning metal (M2) layer 434 is performedto form source electrode, drain electrode and data lines. In thisembodiment, the source and drain electrodes pass through the first andsecond passivation layers 420 and 422 to electrically connect to theactive layer 408. The buffer layer 406 could be a single layer ormulti-layers.

TFT substrate 400 also incorporates a reflective structure 430, whichdefines a sub-pixel location for the placement of one or more LEDs. Inthis embodiment, first insulating layer 436-1 is deposited andsubsequently etched to form contact via 432 in the insulating layer436-1. Then second insulating layer 436-2 is deposited and subsequentlyetched to form opening 438 in the second insulating layer 436-2. A metal(M3) layer 440 is then deposited within opening 438 to form thereflective structure 430, as well as common lines (e.g., common line442), and is also deposited within the contact via 432. The reflectivestructure 430 is used for electrically connecting to a second electricalcontact of the associated display device and a corresponding TFT throughthe contact via 432. An optional bonding (M4) layer 444 may be providedat the sub-pixel location over reflective structure 430 to facilitatebonding of the LEDs.

An example embodiment of a carrier substrate 450 is depicted in FIG. 7.As shown, carrier substrate 450 includes a substrate 452 with a bondinglayer 454 disposed over a top surface 456 of the substrate 452. LEDs(e.g., LEDs 458 and 460) are attached to substrate 452 by bonding layer454. An example of a material for forming the bonding layer 454 is a lowmelting temperature metal, metal alloy, conductive polymer, orcombination thereof. (e.g., a melting temperature below 350° C.,preferably, below 200° C.).

In this embodiment, the LEDs are removably attached to substrate 452with the bonding material adhering to respective second electricalcontacts (462, 464) of the LEDs. Release of the LEDs from carriersubstrate 450 is facilitated by heating the bonding material as will bedescribed in detail later.

As shown in the schematic of FIG. 8, an insulating layer 502 ofappropriate thickness (t) is provided to establish adequate mechanicalclearance between the operational surfaces of transfer components usedin transferring LEDs to a TFT substrate and the upper surfaces of theTFT substrate itself. In particular, a portion of a TFT substrate 500 isdepicted that includes an insulating layer 502, a reflective structure504, and a transfer head 506 of pick-and-place equipment.

When placing LEDs at sub-pixel location 508 (defined by reflectivestructure 504), transfer head 506 typically approaches TFT substrate 500in a downward motion such that a closest distance between theoperational surface 510 of the transfer head and TFT substrate 500 isexhibited with top surface 512 of insulating layer 502. Because of thepotential for inadvertent contact during this placement operation, aclearance is established by setting the position of the top surface 512of the insulating layer 502 relative to a maximum elevation of the LEDswith respect to the TFT substrate.

In this example, the maximum elevation of LEDs 520, 522 is set at theheight of the top surface 524 of a representative one of the LEDs. Aratio of the thickness (t) of insulating layer 502 (t being measuredbetween a bottom surface 526 and a top surface 512) and a distance (d)measured between top surface 512 and the maximum elevation 524 would bewithin a range (R). In this embodiment, the range (R) is betweenapproximately 3% of the thickness (t) and approximately 70% of thethickness (t) of the insulating layer 502, thus ensuring that the topsurfaces of the LEDs protrude upwardly beyond the top surface 512 of theinsulating layer 502 to provide adequate mechanical clearance foroperational surface 510 of the transfer head to prevent transfer headdamaging the insulating layer or the TFT substrate. In an embodiment,the range (R) is between approximately 3% of the thickness (t) andapproximately 25% of the thickness (t) of the insulating layer 502. Inan embodiment, the range (R) is between approximately 3% of thethickness (t) and approximately 15% of the thickness (t) of theinsulating layer 502. In an embodiment, the range (R) is betweenapproximately 40% of the thickness (t) and approximately 70% of thethickness (t) of the insulating layer 502. Further, in anotherembodiment, the thickness (t) can be measured a portion of theinsulating layer above the gate electrode or gate/scan line.

FIGS. 9 and 10 are schematic diagrams depicting representative teststhat may be performed on a carrier substrate prior to removing theassociated LEDs for placement on a TFT substrate. As shown in FIG. 9,carrier substrate 550 includes multiple LEDs (e.g., LEDs 552 and 554)that may be arranged in an array, with each being are removably attachedto the carrier substrate by a bonding layer 556. Test equipment 558 ispositioned adjacent to the LEDs to conduct photoluminescence testing ofone or more of the LEDs.

In FIG. 10, test equipment 560 is positioned to conductelectroluminescence testing of one or more of the LEDs of carriersubstrate 550. It should be noted that various testing may befacilitated in this embodiment owing to conductive properties of bondinglayer 556, which enables the LEDs to be energized in a testing circuit.By using one or more testing procedures such as photoluminescence andelectroluminescence testing while the LEDs are attached to the carriersubstrate, the LEDs may be confirmed as either “good” or “defective”prior to placement.

Continuing with the example embodiment of FIGS. 9 and 10, removal of theLEDs will now be described with respect to FIGS. 11A and 11B. As shownin FIG. 11A, carrier substrate 550 has been loaded onto a platform 562to facilitate LED transfer and placement. Platform 562 incorporates aheater 564 for heating the carrier substrate and the associated bondinglayer 556 to a temperature that facilitates release of the LEDs 552, 554from the carrier substrate.

An array of transfer heads is positioned over the LEDs. In thisembodiment, a heater 566 also is incorporated with the transfer headarray 569. As is shown, transfer head 568 of transfer head array 569 ispositioned over LED 552 and transfer head 570 of transfer head array 569is positioned over LED 554. After transfer head positioning, thetransfer heads are placed in contact with the LEDs for transferring theLEDs to a TFT substrate. Various transfer techniques may be used forselectively retaining (i.e., picking) the LEDs with the transfer heads.By way of example, vacuum, static electricity or magnetic force, amongothers, may be used. Then, as shown in FIG. 11B, transfer heads 568, 570pick up LEDs 552 and 554, respectively, after bonding layer 556 has beenheated by one or both of heaters 564, 566 to a suitable temperature. Itshould be noted that bonding material (e.g., material 572, 574) mayadhere to and be carried by the LEDs after removal from the carriersubstrate.

In FIGS. 12A and 12B, placement of the picked LEDs 552, 554 is shownwith respect to two example embodiments of a TFT substrate.Specifically, FIG. 12A depicts a TFT substrate 580 with a bottom gateTFT 592 configuration and FIG. 12B depicts a TFT substrate 600 with atop gate TFT 692 configuration, although various other configurationsmay be used.

As shown in FIG. 12A, TFT substrate 580 is disposed on platform 562 overa heater 582. In this embodiment, a material of the active layer of thebottom gate TFT configuration may comprise amorphous silicon (a-Si),metal oxide (ex. IGZO), or other suitable material. TFT substrate 580includes a plurality of sub-pixel locations of which one (i.e.,sub-pixel location 584) is shown. Sub-pixel location 584 is defined byreflective structure 586, which is formed in an opening 588 ofinsulating layer 590.

In transferring the LEDs (552, 554) to TFT substrate 580, the transferheads (568, 570) position the LEDs so that a corresponding one or moreof the plurality of LEDs is disposed at each of the plurality ofsub-pixel locations of the TFT substrate. In some embodiments, such asin the embodiment of FIG. 12A, this involves ensuring that at least twoLEDs are disposed over the corresponding reflective structure at each ofthe sub-pixel locations. Thus, in this example, LEDs 552 and 554 aredisposed over reflective structure 586 at sub-pixel location 584. Notealso that a second electrical contact 591 of LED 552 is placed toelectrically contact reflective structure 430 and/or the optionalbonding layer 444, and a second electrical contact 593 of LED 554 isplaced to electrically contact reflective structure 430 and/or theoptional bonding layer 444. Heaters 582 and/or 566 may be used to heatbonding material 572, 574 for fixing the positions of the LEDs withrespect to TFT substrate 580. Note that the reflective structure or theoptional bonding layer is electrically connected to the source/drainelectrodes of the corresponding TFT.

As shown in FIG. 12B, TFT substrate 600 is disposed on platform 562 overheater 582. In this embodiment, a material of the active layer of thetop gate TFT configuration may comprise low temperature polysilicon(LTPS), or other suitable material. After top gate TFT 692 formed on thesubstrate, a first insulating layer 610-1 deposited. The firstinsulating layer 610-1 could be a planarization layer. Then a secondinsulating layer is disposed on the first insulating layer 610-1 andforming an opening 608 in the second insulating layer 610-2. TFTsubstrate 600 includes a plurality of sub-pixel locations, with onlysub-pixel location 604 being shown. Sub-pixel location 604 is defined byreflective structure 606, which is formed in the opening 608 of secondinsulating layer 610-2.

For transferring the LEDs (552, 554) to TFT substrate 600, the transferheads (568, 570) position over the LEDs so that a corresponding one ofthe plurality of LEDs is disposed at each of the plurality of sub-pixellocations of the TFT substrate. In this embodiment, LEDs 552 and 554 aredisposed over reflective structure 606 at sub-pixel location 604.Specifically, a second electrical contact 611 of LED 552 is placed toelectrically contact reflective structure 606 and/or bonding material612, and a second electrical contact 613 of LED 554 is placed toelectrically contact reflective structure 606 and/or bonding material614. Heaters 582 and/or 562 are used to heat bonding material 612, 614to fix the positions of the LEDs with respect to TFT substrate 600. Inthis example, as shown in FIG. 12B, the maximum elevation of LEDs 552,554 is set at the height of the top surface of a representative one ofthe LEDs. A ratio of the thickness (t2) measured between a bottomsurface 610-3 of second insulating layer and a top surface 610-4 ofsecond insulating layer and a distance (d2) measured between top surface610-4 and the top surface 552-1 of the LED 552 would be within a range(R). In an embodiment, the range (R) is between approximately 3% of thethickness (t2) and approximately 70% of the thickness (t2) of the secondinsulating layer 610-2, thus ensuring that the top surfaces 552-1 of theLEDs protrude upwardly beyond the top surface 610-4 of the secondinsulating layer 610-2 to provide adequate mechanical clearance for thetransfer head to prevent transfer head damaging the second insulatinglayer or the TFT substrate. In an embodiment, the range (R) is betweenapproximately 3% of the thickness (t) and approximately 25% of thethickness (t) of the insulating layer 502. In an embodiment, the range(R) is between approximately 3% of the thickness (t) and approximately15% of the thickness (t) of the insulating layer 502. In an embodiment,the range (R) is between approximately 40% of the thickness (t) andapproximately 70% of the thickness (t) of the insulating layer 502.Further, in another embodiment, the thickness (t) can be measured aportion of the insulating layer above the gate electrode or gate/scanline.

FIGS. 13A and 13B are schematic diagrams depicting example embodimentsof testing of LEDs disposed on TFT substrates such as may be performedafter the LEDs are transferred from a carrier substrate and fixed inposition. Continuing with the example shown and described with respectto FIG. 12A, test equipment 620 is positioned adjacent to LEDs 552 and554 to conduct photoluminescence testing of one or more of the LEDs ofTFT substrate 580. Additionally, or alternatively, electroluminescencetesting of one or more of the LEDs may be conducted. An example ofelectroluminescence testing is depicted in FIG. 13B, in which testequipment 630 is positioned adjacent to LEDs 552 and 554 of TFTsubstrate 600. By using one or more testing procedures such asphotoluminescence and electroluminescence testing, the LEDs may beconfirmed as either “good” or “defective”.

After performing testing, the TFT substrate may be transferred to adeposition chamber (not shown) for further fabrication. In this regard,multiple processes will now be described using the embodiment of FIG.13A (i.e., TFT substrate 580) for reference. It should be noted thatthese processes may be suited for use with other configurations of TFTsubstrates.

As shown in FIG. 14, a filling insulator 640 is deposited at thesub-pixel locations. Filling insulator 640 may be formed of transparentmaterial, such as epoxy, PMMA, benzocyclobutene (BCB), polyimide orcombination thereof, for example. In FIG. 14, filling insulator 640 atleast partially fills the opening 588 lined by reflective structure 586.As such, filling insulator 640 fills between LEDs 552 and 554, andbetween the LEDs and reflective structure 586. In this embodiment,filling insulator 640 extends over the second electrical contacts (591,593) of the LEDs and up the side walls (e.g., side walls 642 and 644) ofthe LEDs. In other embodiments, filling insulator 640 may only extendover the second electrical contacts (591, 593) of the LEDs for isolatingthe second electrical contact from other conducting material.

As mentioned above, if it is determined that an LED is defective, arepair may be performed. As shown in FIG. 15, an example of a repair isdepicted in which a passivation layer 650 is deposited over a defectiveLED (in this case, LED 552). In particular, LED 552 includes a firstelectrical contact 652, and LED 554 includes a first electrical contact654. A passivation layer 650 is provided over first electrical contact652 of LED 552 to electrically isolate the first electrical contact froma first electrode (shown later) of the display device in which TFTsubstrate 580 is to be incorporated. In another embodiment, thedefective LED could be replaced by a “good” LED, such as when only oneLED is provided for a sub-pixel, for example.

As shown in FIG. 16, after any defects are repaired as desired, a firstelectrode 660 may be deposited. The first electrode provideselectrically connects the LEDs and associated common lines (e.g., commonline 662).

With reference to the embodiment of FIG. 17A, it is shown that the firstelectrode 660 may be patterned to provide discontinuous portions forinterconnecting separate groups of the sub-pixels and the common line662. For instance, sub-pixel 670, which includes LEDs 552 and 554, isassociated with first electrode portion 672, which also provideselectrical continuity for sub-pixels 674, 675, 676, 677 and 678. Firstelectrode portion 680, however, is patterned so that electricalconnection with at least one LED of a sub-pixel is avoided and thepassivation layer 650 could be omitted in this embodiment. For example,sub-pixel 682 includes LEDs 684 and 686, with first electrode portion680 only electrically connecting LED 686. In some embodiments, an LEDavoided by a first electrode portion may be a defective LED.

FIG. 17B depicts another example embodiment in which a first electrodehas been deposited. In contrast to the patterned variant of FIG. 17A,this embodiment incorporates a contiguous first electrode 690 after thepassivation layer 650 is deposited.

Continuing for ease of description (in a non-limiting manner) with theembodiment of FIG. 16, FIG. 18 shows TFT substrate 580 afterincorporating a light guide layer 700. In particular, a light guidelayer 700 is deposited over first electrode 660. The light guide layer700 allows the light emitted from an LED to spread out. By using thelight guide layer may increase total light emission toward a determineddirection (e.g., a viewing direction), increase emission uniformity,and/or increase sharpness of the color spectrum for the display.

In FIG. 19, a wavelength conversion layer 710 is provided over firstelectrode 660. In particular, wavelength conversion layer 710 (which maybe of various configurations, such as quantum dot, phosphor orcombination thereof, for example), is formed over light guide layer 700in this embodiment. The wavelength conversion layer can convert thewavelength of light emitted from the LED to a target wavelength. Forinstance, if each LED is to emit only one color spectrum (e.g., all LEDsemit blue light), different wavelength conversion layers can convert thesingle color spectrum to red, green, blue or other color spectrum.

As shown in FIG. 20, a color filter 720 is provided over first electrode660. Specifically, in this embodiment, color filter 720 is positionedover an optical adhesion layer 722 that is used to adhere color filter720 to TFT substrate with LEDs. A cover 730 (e.g., a rigid or flexiblecover substrate; a glass cover, polarizer, barrier film or cappinglayer) is provided as a top layer of the structure. The color filterlayer can filter out undesired colors emitting from the wavelengthconversion layer and sharpen the emission spectrum of light. By way ofexample, a red color filter layer may be formed over a red wavelengthconversion layer in order to filter out colors other than red; a greencolor filter layer may be formed over a green wavelength conversionlayer in order to filter out colors other than green; and, a blue colorfilter layer may be formed over a blue wavelength conversion layer inorder to filter out colors other than blue. It should be noted that thelight guide layer, the wavelength conversion layer and the color filterlayer are optional and could be selected as desired.

Another example embodiment is depicted in FIG. 21, in which a TFTsubstrate 800 configured with an top gate TFT 802 is provided. As shownin FIG. 21, TFT substrate 800 includes a substrate 804 upon which abuffer layer 806 and an active layer 808 are formed. In this embodiment,the buffer layer 806 is multi-layers. The buffer layer could be a singlelayer in other embodiments. Re-crystallization (e.g., by excimer laserannealing), patterning to form the channel 810, and channel/N+ dopingare performed. Gate insulation layer 812 and metal (M1) layer 814 aresubsequently deposited and patterned to form gate electrode and gatelines. Thereafter, first and second passivation layers (820, 822) aredeposited. The gate insulation layer 812, the first passivation layer,or the second passivation layer could be a single layer or multi-layers.

Depositing and patterning metal (M2) layer 834 is performed to formsource electrode, drain electrode and data lines. First insulating layer836-1 is deposited and contact via 832 is formed and pass through thefirst insulating layer 836-1. Then second insulating layer 836-2 isdeposited and subsequently etched to form opening 838 in the secondinsulating layer 836-2. A metal (M3) layer 840 is then deposited withinopening 838 to form the reflective structure 830, as well as commonlines (e.g., common line 842). The metal (M3) layer 840 is also disposedinto the contact via 832. Reflective structure 830 may be used forelectrically connecting to a second electrical contact of the associateddisplay device and a corresponding TFT through the contact via 832. Anoptional bonding (M4) layer 844 may be over reflective structure 830 tofacilitate bonding of the LEDs.

FIG. 21 also depicts a filling insulator 845 that fills between LEDs 850and 852, and between the LEDs and reflective structure 830. A defectrepair also is shown that is facilitated by deposition of a passivationlayer 846 to electrically isolate a first electrical contact 848 of“defective” LED 850 from first electrode 860. Additionally, a lightguide layer 870, a wavelength conversion layer 880, and a color filter890 are provided over first electrode 860. In this embodiment, colorfilter 890 is positioned over an optical adhesion layer 892. A cover 894also is provided as a top layer of the structure. The cover 894 could bea rigid or flexible substrate, e.g., a glass cover, a polarizer, abarrier film or capping layer (inorganic-organic-inorganic layers). Itshould be noted that the light guide layer, the wavelength conversionlayer and the color filter layer are optional and could be selected asdesired.

A material of passivation layers mentioned above may comprise inorganicmaterial, organic material. A material of insulating layers mentionedabove may comprise inorganic material, organic material, a light shieldmaterial or combination thereof. And a material of filling insulatormentioned above may comprise inorganic material, organic material, alight shield material or combination thereof. For example, the organicmaterial can comprise a polymer, such as polyethylene terephthalate(PET), polyimide, polycarbonate, epoxy, polyethylene, and/or apolyacrylate, and the inorganic layer can comprise SiOx, SiNx, SiOxNy,TiO2, AlOx, Al2O3, SrOx or combination thereof.

FIG. 22 is a schematic view of another example embodiment of a carriersubstrate showing removal of an LED; in this case, a flip-chip type LED.In FIG. 22, carrier substrate 950 has been loaded onto a platform 962 tofacilitate LED transfer and placement. Platform 962 incorporates aheater 964 for heating the carrier substrate 950 and the associatedbonding layer 970 to a temperature that facilitates release of LED 952from the carrier substrate.

An array of transfer heads is positioned over the carrier substrate. Inthis embodiment, a heater 966 also is incorporated with the transferheads (one of which is shown). In particular, transfer head 968 ispositioned over LED 952 and the transfer head is placed in contact withthe LED for transferring the LED to a TFT substrate. It should be notedthat, the heater is optional.

Transfer of the LEDs (e.g., LED 952) may be performed as describedbefore resulting in bonding material from a bonding layer 970 adheringto electrical contacts of the LED after the LED is removed from thecarrier substrate. Specifically, bonding material 972 adheres to secondelectrical contact 974 and bonding material 976 adheres to firstelectrical contact 978. The first electrical contact 978 could beelectrically connected to the common line, and the second electricalcontact 974 could be electrically connected to the drain electrode ofthe corresponding TFT of the sub-pixel.

Continuing with the embodiment of FIG. 22, placement of the LEDs fromcarrier substrate 950 is shown in FIG. 23 (which depicts a plan orlayout view) and FIG. 24 (which depicts a cross-sectional view). Asshown in FIGS. 23 and 24, LEDs 952, 954 are incorporated into a displaydevice 1000 that is configured with a top gate TFT 1002 (e.g., LTPSTFT). Display device 1000 includes a TFT substrate 1004 upon which abuffer layer 1006 and an active layer 1008 are formed. In thisembodiment, the buffer layer 1006 is multi-layers. The buffer layercould be a single layer in other embodiments. Re-crystallization,patterning to form the channel 1010, and channel/N+ doping areperformed. Gate insulation layer 1012 and metal (M1) layer 1014 aredeposited and patterned to form gate electrode and gate lines.Thereafter, first and second passivation layers (1020, 1022) aredeposited. The gate insulation layer, the first passivation layer, orthe second passivation layer could be a single layer or multi-layers.

Depositing and patterning metal (M2) layer 1034 is performed to formsource electrode, drain electrode and data lines. First insulating layer1036-1 is deposited and then contact via 1032 is formed. Then secondinsulating layer 1036-2 is deposited and subsequently etched to formopening 1038 in the second insulating layer 1036-2. A metal (M3) layer1040 is then deposited within opening 1038 to form reflective structure,as well as common lines (e.g., common line 1042). And the metal (M3)layer 1040 is also disposed into the contact via 1032. In thisembodiment, the reflective structure 1030 is formed by separate portions(shown more clearly in FIG. 23), with reflective portion 1031functioning as an anode and electrically connecting to second electricalcontact 974 of LED 952, reflective portion 1033 serving as a connectionfrom first electrical contact 978 of LED 952 to common line 1042, andreflective portion 1035 serving as a connection from first electricalcontact of LED 954 to common line 1042. A filling insulator 1045 atleast partially fills between LEDs 952 and 954, and between the LEDs andreflective structure 1030 to stabilize the positions of LEDs 952 and954.

In FIG. 24, a defect repair also is shown that is facilitated by lasercutting the M3 layer to electrically isolate first electrical contact978 of “defective” LED 952 from a common line 1042 of the displaydevice. In this embodiment, laser cutting is performed at aninterconnect portion 1037 of the M3 layer that extends between thereflective portion 1033 and common line 1042 (note that the lasercutting is depicted by arrow L)

Additionally, a light guide layer 1070, a wavelength conversion layer1080, and a color filter 1090 are provided. In this embodiment, colorfilter 1090 is positioned over an optical adhesion layer 1092. A cover1094 also is provided as a top layer of the structure. The cover 1094could be a rigid or flexible substrate, e.g., a glass cover, apolarizer, a barrier film or capping layer (inorganic-organic-inorganiclayers). It should be noted that the light guide layer, the wavelengthconversion layer and the color filter layer are optional and could beselected as desired.

Another embodiment of an LED that may be used in cooperation with aboveembodiments is depicted in FIG. 25. As shown in FIG. 25, LED 1100 is ahybrid device that incorporates a second electrical contact 1102 and afirst electrical contact 1104. LED 1100 may include a first conductivesemiconductor layer 1117, a multi quantum well layer 1115 formed on thefirst conductive semiconductor layer 1117, and a second conductivesemiconductor layer 1113 formed on the multi quantum well layer 1115.Note that the second electrical contact 1102 is positioned at the bottomof the device, whereas the first electrical contact 1104 includes aportion 1105 positioned at the bottom as well as a portion 1107positioned adjacent to the top of the device. The first conductivesemiconductor layer 1117 and the second conductive semiconductor layer1113 may be a p-type semiconductor layer and n-type semiconductor layer,respectively. An undoped semiconductor layer 1111 may be formed on thesecond conductive semiconductor layer 1113.

The conductive protection layer 1109 may protect the first electricalcontact 1104 from laser beams used to separate an LED growth substrate(e.g., sapphire substrate) and an LED 1100 during a laser lift offprocess. The conductive protection layer 1109 is formed of a materialfor absorbing laser beams (band gap of conductive protection layer issmaller than that of laser beams during laser lift off process). Forinstance, the conductive protection layer may be formed of Indium TinOxide (ITO), ZnO, SnO₂, or TiO₂. It should be emphasized that theabove-described embodiments are merely examples of possibleimplementations. Many variations and modifications may be made to theabove-described embodiments without departing from the principles of thepresent disclosure. All such modifications and variations are intendedto be included herein within the scope of this disclosure.

What is claimed is:
 1. A method for manufacturing a display devicecomprising: providing a thin film transistor (TFT) substrate having aplurality of sub-pixel locations and a plurality of TFTs correspondingto the plurality of sub-pixel locations; providing a carrier substratesupporting a plurality of light emitting diodes (LEDs), wherein each ofthe plurality of LEDs has a first electrical contact and a secondelectrical contact; transferring the plurality of LEDs from the carriersubstrate to the TFT substrate, with at least two of the plurality ofLEDs being disposed at one of the plurality of sub-pixel locations; andfixing positions of the plurality of LEDs with respect to the TFTsubstrate.
 2. The method of claim 1, further comprising: providing afilling insulator at the one of the plurality of sub-pixel locations,wherein the filling insulator fills between the at least two of theplurality of LEDs disposed at the one of the plurality of sub-pixellocations.
 3. The method of claim 2, further comprising: determiningthat one of the at least two of the plurality of LEDs at the one of theplurality of sub-pixel locations is defective; and electricallyisolating the one of the at least two of the plurality of LEDsdetermined to be defective.
 4. The method of claim 3, wherein theelectrically isolating comprises providing a passivation layer over thefirst electrical contact of the one of the at least two of the pluralityof LEDs determined to be defective.
 5. The method of claim 3, furthercomprising forming a first electrode over the plurality of LEDs.
 6. Themethod of claim 5, wherein the one of the plurality of LEDs determinedto be defective is not covered by the first electrode.
 7. The method ofclaim 6, further comprising providing at least one of a color filter anda wavelength conversion layer over the first electrode layer.
 8. Themethod of claim 1, wherein, in providing the TFT substrate, a firstelectrode is disposed at the one of the plurality of sub-pixellocations.
 9. The method of claim 8, further comprising: determiningthat one of the at least two of the plurality of LEDs at the one of theplurality of sub-pixel locations is defective; and laser cutting thefirst electrode disposed at the one of the plurality of sub-pixellocations.
 10. The method of claim 1, wherein: in providing the TFTsubstrate, the one of the plurality of sub-pixel locations has acorresponding reflective structure; and in transferring the plurality ofLEDs from the carrier substrate to the TFT substrate, the at least twoof the plurality of LEDs are disposed over the corresponding reflectivestructure at the one of the plurality of sub-pixel locations.
 11. Themethod of claim 10, wherein: in providing the TFT substrate, aninsulating layer is provided; after the fixing positions of theplurality of LEDs, the plurality of LEDs exhibit a maximum elevationwith respect to the TFT substrate; and a top surface of the insulatinglayer is positioned to be lower than the maximum elevation.
 12. Themethod of claim 11, wherein: the insulating layer is provided at athickness (t) extending between a bottom surface of the insulating layerand a top surface of the insulating layer; and a distance (d) betweenthe top surface of the insulating layer and the maximum elevation isbetween approximately 3% of the thickness and approximately 70% of thethickness.
 13. A method for manufacturing a display device comprising:providing a thin film transistor (TFT) substrate having a plurality ofsub-pixel locations and a plurality of TFTs; providing a carriersubstrate supporting a plurality of light emitting diodes (LEDs),wherein each of the plurality of LEDs has a first electrical contact anda second electrical contact; transferring the plurality of LEDs from thecarrier substrate to the TFT substrate, with a corresponding one of theplurality of LEDs being disposed at each of the plurality of sub-pixellocations; fixing positions of the plurality of LEDs with respect to theTFT substrate; and providing a filling insulator contacting sidewalls ofthe plurality of LEDs.
 14. The method of claim 13, after the fixingpositions of the plurality of LEDs, further comprising: determining thata first LED of the plurality of LEDs is defective; and electricallyisolating the first electrical contact of the first LED determined to bedefective.
 15. The method of claim 14, wherein a first electrode of thedisplay device is not disposed over the first LED determined to bedefective.
 16. The method of claim 14, wherein electrically isolatingthe first electrical contact comprises providing a passivation layerover the first electrical contact of the first LED.
 17. The method ofclaim 14, wherein electrically isolating the first electrical contactcomprises laser cutting a first electrode of the display device.
 18. Themethod of claim 13, wherein, in transferring the plurality of LEDs, atleast two of the plurality of LEDs are disposed at each of the pluralityof sub-pixel locations.
 19. The method of claim 13, wherein: inproviding the TFT substrate, an insulating layer is provided; after thefixing positions of the plurality of LEDs, the plurality of LEDs exhibita maximum elevation with respect to the TFT substrate; and a top surfaceof the insulating layer is positioned to be lower than the maximumelevation.
 20. The method of claim 19, wherein: the insulating layer isprovided at a thickness (t) extending between a bottom surface of theinsulating layer and a top surface of the insulating layer; and adistance (d) between the top surface of the insulating layer and themaximum elevation is between approximately 3% of the thickness andapproximately 70% of the thickness.